Full circle programming in CNC Programming - Step-by-Step Execution

Concept Flow - Full circle programming

Start at circle start point or reference point

↓

Move to circle start point

↓

Define circle radius and direction

↓

Execute circular interpolation command

↓

Complete full 360-degree circle

↓

Return to start or next operation

This flow shows how a CNC machine moves from a start point, defines a circle, and executes a full circular path.

Execution Sample

CNC Programming

G17 G90 G02 X0 Y0 I10 J0 F100

This CNC command programs a full circle clockwise with radius 10 units starting from current position.

Execution Table

Step	Command Part	Action	Position (X,Y)	Radius (I,J)	Feed Rate	Output
1	G17	Select XY plane	(0,0)	(unchanged)	(unchanged)	Plane set to XY
2	G90	Set absolute positioning	(0,0)	(unchanged)	(unchanged)	Positioning mode: Absolute
3	G02	Set circular interpolation clockwise	(0,0)	(unchanged)	(unchanged)	Interpolation mode: Clockwise
4	X0 Y0	Specify circle end point	(0,0)	(unchanged)	(unchanged)	Circle end point set to (0,0)
5	I10 J0	Set circle center offset	(0,0)	(10,0)	(unchanged)	Circle center offset set
6	F100	Set feed rate	(0,0)	(10,0)	100	Feed rate set to 100 units/min
7	Execute circle	Machine moves full circle clockwise	(0,0)	(10,0)	100	Full circle completed
8	End	Program ends or next command	(0,0)	(10,0)	100	Program ready for next operation

💡 Full circle completed at position (0,0) with radius 10, feed rate 100

Variable Tracker

Variable	Start	After Step 4	After Step 5	After Step 6	After Step 7	Final
Position (X,Y)	(0,0)	(0,0)	(0,0)	(0,0)	(0,0)	(0,0)
Radius Offset (I,J)	(none)	(none)	(10,0)	(10,0)	(10,0)	(10,0)
Feed Rate	(default)	(default)	(default)	100	100	100
Interpolation Mode	(default)	Clockwise	Clockwise	Clockwise	Clockwise	Clockwise
Plane	(default)	XY	XY	XY	XY	XY
Positioning Mode	(default)	Absolute	Absolute	Absolute	Absolute	Absolute

Key Moments - 3 Insights

Why does the machine return to the start point after completing the circle?

Because the circle is a full 360-degree path, the end point matches the start point as shown in step 7 of the execution_table.

What do the I and J values represent in the command?

I and J specify the offset from the start point to the circle center on the X and Y axes respectively, as seen in step 5 of the execution_table.

Why is absolute positioning important in this program?

Absolute positioning (G90) ensures all coordinates are referenced from a fixed origin, preventing unexpected moves, as set in step 2.

Visual Quiz - 3 Questions

Look at the execution_table at step 5, what does the I10 J0 mean?

A Feed rate is 10

B Circle center is 10 units right of start point

C Circle radius is 0

D Machine moves 10 units up

💡 Hint

Check the 'Radius (I,J)' column at step 5 in execution_table

At which step does the machine set the feed rate to 100 units/min?

A Step 3

B Step 4

C Step 6

D Step 7

💡 Hint

Look at the 'Feed Rate' column in execution_table

If we change G02 to G03, what changes in the execution_table?

A Interpolation mode changes to Counterclockwise

B Feed rate changes

C Position changes immediately

D Plane changes to XZ

💡 Hint

Check the 'Interpolation Mode' row in variable_tracker and step 3 in execution_table

Concept Snapshot

Full circle programming uses G02 (clockwise) or G03 (counterclockwise) commands.
I and J specify the circle center offset from start point.
X and Y specify the circle end point.
G90 sets absolute positioning.
Feed rate (F) controls speed.
Completes a 360-degree circular path returning to start.

Full Transcript

Full circle programming in CNC involves moving the tool in a complete circular path. The program starts by selecting the XY plane (G17) and setting absolute positioning (G90). The circular interpolation command G02 is used for clockwise motion. The X and Y values set the circle's end point, while I and J specify the center offset from the start point, defining the radius. The feed rate F controls the speed of the movement. The machine executes the full circle, returning to the start point. This process ensures precise circular cuts or movements in CNC machining.

Practice

1. What does the G02 command do in full circle CNC programming?

easy

A. It turns the spindle on.

B. It cuts a counterclockwise arc or circle.

C. It sets the machine to absolute positioning mode.

D. It cuts a clockwise arc or circle.

Solution

1. Step 1: Understand G02 command purpose

   G02 is used to cut arcs or circles in a clockwise direction.

2. Step 2: Compare with other commands

   G03 cuts arcs counterclockwise, so G02 must be clockwise.

3. Final Answer:

   It cuts a clockwise arc or circle. -> Option D

4. Quick Check:

   G02 = Clockwise arc [OK]

Hint: G02 = Clockwise arc, G03 = Counterclockwise arc [OK]

Common Mistakes:

• Confusing G02 with G03 direction
• Thinking G02 sets positioning mode
• Assuming G02 turns spindle on

2. Which of the following is the correct syntax to program a full clockwise circle with radius 10 ending at (X0, Y0) using G02?

easy

A. G02 X0 Y0 I10 J0 F100

B. G02 X0 Y0 I0 J10 F100

C. G02 X0 Y0 I-10 J0 F100

D. G02 X0 Y0 I0 J-10 F100

Solution

1. Step 1: Understand I and J parameters

   I and J specify the center offset from the start point in X and Y directions respectively. For radius 10 on X-axis, I=10, J=0.

2. Step 2: Check direction and feedrate

   G02 is clockwise, feedrate F100 is valid. So syntax with I10 J0 is correct.

3. Final Answer:

   G02 X0 Y0 I10 J0 F100 -> Option A

4. Quick Check:

   Center offset I=10, J=0 for radius 10 [OK]

Hint: I and J are center offsets; positive I means right of start [OK]

Common Mistakes:

• Swapping I and J values
• Using negative radius offsets incorrectly
• Omitting feedrate F

3. What will be the result of this CNC code snippet?

G90
G21
G00 X0 Y0
G02 X0 Y0 I10 J0 F150

medium

A. The code will cause a syntax error and stop.

B. The machine will move in a straight line to X10 Y0.

C. The machine will cut a full clockwise circle with radius 10 at origin.

D. The machine will cut a counterclockwise arc with radius 10.

Solution

1. Step 1: Analyze positioning and units

   G90 sets absolute positioning, G21 sets units to millimeters.

2. Step 2: Interpret G02 command

   G02 with X0 Y0 and I10 J0 means cut a clockwise arc starting and ending at origin with center offset 10mm in X, making a full circle.

3. Final Answer:

   The machine will cut a full clockwise circle with radius 10 at origin. -> Option C

4. Quick Check:

   G02 with same start/end and I/J offset = full circle [OK]

Hint: Same start/end point with I/J offset = full circle [OK]

Common Mistakes:

• Thinking G02 moves in straight line
• Confusing clockwise with counterclockwise
• Assuming syntax error due to zero end point

4. Identify the error in this full circle CNC program snippet:

G90
G21
G03 X0 Y0 I10 J0 F100

medium

A. Start and end points are the same but I and J do not form a valid circle center.

B. I and J values should be negative for G03.

C. Feedrate F100 is missing.

D. G03 cannot be used for full circles.

Solution

1. Step 1: Check start and end points

   Start and end points are both at X0 Y0, which is valid for full circle.

2. Step 2: Validate I and J center offsets

   I=10 J=0 means center is 10 units right of start. For a full circle, the center must be correctly offset to form a circle. Here, the center offset is valid, but the direction G03 is counterclockwise, so the path may not complete correctly if the machine expects a different center.

3. Step 3: Identify the actual problem

   In many CNC controls, for a full circle with G03, the center offset must be negative or adjusted to match the direction. Using I10 J0 with G03 causes an invalid arc path.

4. Final Answer:

   I and J values should be negative for G03. -> Option B

5. Quick Check:

   Center offset must match arc direction [OK]

Hint: Center offsets must match arc direction for full circles [OK]

Common Mistakes:

• Assuming feedrate is missing
• Thinking G03 can't do full circles
• Using wrong sign for I/J without checking direction

5. You want to program a full circle of radius 15 mm centered at X20 Y20 using G03 (counterclockwise). The start point is at X35 Y20. Which is the correct G-code line to cut this circle?

hard

A. G03 X35 Y20 I-15 J0 F120

B. G03 X35 Y20 I15 J0 F120

C. G03 X35 Y20 I0 J-15 F120

D. G03 X35 Y20 I0 J15 F120

Solution

1. Step 1: Determine center offset from start point

   Start point is X35 Y20, center is X20 Y20. Offset I = centerX - startX = 20 - 35 = -15, J = 20 - 20 = 0.

2. Step 2: Match arc direction with offsets

   G03 is counterclockwise, so negative I offset is correct to go around center counterclockwise.

3. Final Answer:

   G03 X35 Y20 I-15 J0 F120 -> Option A

4. Quick Check:

   Center offset I = -15 matches start and center [OK]

Hint: Center offset = center - start; sign matters for direction [OK]

Common Mistakes:

• Using positive I when negative is needed
• Swapping I and J values
• Ignoring start point coordinates